Process and system for treating particulate solids

ABSTRACT

System and method for treating particulate solids comprises a screw feeder for transporting a water-based slurry of contaminated particulate solids through an ultrasound signal of sufficient size, strength and duration to cause the contaminants to separate from the particulate solids. One or more stacks of ultrasonic transducers arranged around the screw feeder may be employed in which the diameter of each transducer preferably is substantially the same as the pitch of the screw feeder.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/536,794, filed Sep. 20, 2011, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the treatment of the class of solidmaterials called particulates that includes assemblies of matter inindividual units of size of about one inch or less.

2. Background Description and Brief Discussion of the Related Art

Particulate matter may have various origins. They may occur in nature,such as metal or petroleum sources, or they may be man-made, such aschips or filaments that are cut from the surfaces of metal bars duringlathe processing. For each of these types, the particulate matter is inneed of some kind of treatment, be it either elimination of acontaminant and impurity or the recovery of a valuable component. Ineither case, removal of a component from the particulate is a necessarystep for a subsequent, value-added product.

For example, titanium machining chips are valuable and are re-melted andrecycled for subsequent use. However, titanium machining chips getcontaminated with a residual cutting oil, and the oil createsmetallurgical problems during melting and casting of the metal.Therefore, it is critical that the oil be removed from the chips beforethey are recycled and reused.

In currently available cleaning systems and processes, the contaminatedchips are washed in a large volume of scalding hot water with very highlevels of caustic cleaning agents. However, such cleaning systems andprocesses disadvantageously result in a liquid by-product of high pH.Such systems and processes also disadvantageously require the cleaningsolution to reach relatively high temperatures, require sufficientcaustic chemical cleaning agents to achieve the desired high pH, andrequire subsequent neutralization treatment of the effluent solution inorder to avoid dealing with a hazardous waste. These requirements,individually and in combination, result in a high treatment cost and arelatively large amount of by-products.

Several cutting-edge alternative processes can be considered in place ofthe cleaning process described above. First, a treatment process mayemploy enzymatic agents; but, while such a process reduces temperaturerequirements and alleviates the waste concerns, the enzymes that arerequired disadvantageously are expensive and are terminal in use as theyare disposed of in the by-product. As another possible technique, thechips may be chemically treated with a strong nitric and hydrofluoricacid solution, but disposal of the liquid by-product would be hazardoussince it would contain quantities of the fluoride ion. As yet anotherpossible technique, titanium chips may be cleaned with a spray of tinyabrasive glass particles, but adhesion of the glass particles to thesurfaces of the oil coated chips reduces the affectivity of thisprocess.

OBJECTIVES AND SUMMARY OF THE INVENTION

In view of the foregoing, it is therefore desirable and thus anobjective of the present invention to provide systems and processes fortreating particulates that result in one or more than one of thefollowing benefits: reduction in the cleaning time; reduction in thetemperatures employed; reduction in the amount of chemical reagentsused; the use of milder cleaning reagents; reduction of the amount ofby-product; and/or the reduction or elimination of the need toneutralize the by-product.

In accordance with the present invention, a system for treatingparticulate solids comprises an ultrasonic transducer producing anultrasound signal, a rotating screw feeder having a portion extendingthrough an active region of the ultrasound signal produced by theultrasonic transducer, the screw feeder having a plurality of flightseach separated from one another by a predetermined distance, called thepitch, that is no greater than a width of the active region of theultrasound signal, and a slurry including water and the particulatesolids disposed within the screw feeder in which the particulate solidsare contained within chambers defined by the flights of the screw feederand move along the screw feeder as the screw feeder rotates, theparticulate solids contained within a chamber disposed within the activeregion of the ultrasound signal being sufficiently agitated by theultrasound signal to cause contaminants to separate from the particulatesolids contained within the chamber.

In accordance with a method embodiment of the present invention, amethod of treating particulate solids comprises the steps of supplying ascrew feeder for transporting contaminated particulate solids, supplyinga continuous flow of water through the screw feeder, supplying theparticulate solids into the screw feeder, the particulate solids and thewater forming a slurry, supplying an ultrasound signal, andtransporting, by the screw feeder, the slurry containing the particulatesolids through the ultrasound signal for a predetermined amount of time,and wherein the ultrasound signal is of sufficient size and strength tocause the contaminants to separate from the particulate solids.

In the system and method embodiments summarized above, various aspectsof the invention are as follows.

As one aspect of the invention, a plurality of ultrasonic transducersare disposed circumferentially around a perimeter of at least a portionof the screw feeder, and each of the ultrasonic transducers produces arespective ultrasound signal.

As another aspect of the invention, a stack of ultrasonic transducersare disposed along a portion of an exterior of the screw feeder, andeach of the ultrasonic transducers produces a respective ultrasoundsignal and has a diameter substantially the same as the pitch of thescrew feeder.

As a further aspect of the invention, the screw feeder, while moving theslurry, provides a turbulence to the slurry to cause the particulatesolids to be stirred and rotated.

As yet another aspect of the invention, the ultrasonic transducerproduces an ultrasound signal having frequencies substantially within arange of 25 kHz and 45 kHz.

As yet a further aspect of the invention, the slurry contains detergentin an amount of substantially no greater than 0.2 weight % of the amountof water.

As yet another aspect of the invention, the slurry contains detergent inan amount of substantially no greater than 1.0 weight % of the amount ofwater.

As yet an additional aspect of the invention, the water is at atemperature not exceeding substantially 120 degrees Fahrenheit.

Still as yet another aspect, at least a portion of the water exitingfrom a water exit end of the screw feeder (e.g., 80% of the water) isrecycled back to a water entrance end of the screw feeder.

As a feature of this aspect, detergent is added to the recycled watersufficient to prevent recontamination to the particulate solids by thecontaminants disposed within the recycled water.

In accordance with another embodiment of the present invention, a systemfor treating particulate solids comprises an ultrasonic transducerproducing an ultrasound signal, a tank having a chamber substantiallyfully disposed within an active zone of the ultrasound signal, a slurryincluding water and the particulate solids, the chamber of the tankcontaining the particulate solids of the slurry within the active zoneof the ultrasound signal, wherein the ultrasound signal agitates theparticulate solids disposed within the entire chamber sufficient tocause contaminants to separate from the particulate solids.

Various aspects summarized above also are applicable to this systemembodiment.

Various other objectives, advantages and features of the presentinvention will become readily apparent to those of ordinary skill in theart, and the novel features will be particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the present invention solely thereto, will best beappreciated in conjunction with the accompanying drawings, wherein likereference numerals denote like elements and parts, in which:

FIG. 1 is a schematic illustration of a screw feeder used to describethe screw feeder embodiment of the present invention;

FIG. 2 is another schematic illustration of a screw feeder having aseries of ultrasonic transducers in accordance with the screw feederembodiment of the present invention;

FIG. 3 is a photograph of an exemplary ultrasound tank and a powersupply that may be used with the present invention;

FIGS. 4A through 4D are a series of photographs showing the progress incleaning a sample of titanium chips during the passage of time inaccordance with the present invention;

FIG. 5 is a photograph of a sheet of aluminum foil that has undergone“treatment” within the ultrasound tank of the present invention;

FIG. 6 is a schematic illustration showing a single active zone inaccordance with the present invention;

FIG. 7 is a schematic illustration of the system for treatingparticulate solids in accordance with the screw feeder embodiment of thepresent invention;

FIG. 8 shows a portion of the system for treating particulate solids inaccordance with the screw feeder embodiment of the present invention;

FIG. 9 is a schematic representation of the steady state flow of liquidand chips through the reactor with liquid by-product recycled inaccordance with the present invention;

FIG. 10 shows an exemplary steady state flow of liquid and chips throughthe reactor;

FIG. 11 is a graph showing the calculated oil contents of the liquidby-product as a function of reactor operating time, while employingpartial recycling, in accordance with the present invention;

FIG. 12 is a graph showing the calculated oil contents of the liquidby-product as a function of reactor operating time, while employing fullrecycling, in accordance with the present invention; and

FIG. 13 is a graph showing a downward trend in oil content of liquidby-product as the carbon content of the chips declines for the case of80 percent liquid recycle in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The inventors of the present invention, as part of the company WaveParticle Processing, have produced the herein described apparatuses andmethods to facilitate the removal of materials from particulatesubstrates with the advantageous features mentioned above.

As herein described, the present invention employs ultrasonic transducerstacks in a unique configuration specific to the treatment ofparticulates. In summary, the present invention temporarily confinesparticles of interest, such as contaminated titanium chips, in awater-based slurry containing a small amount of mild detergent, where itis desired to remove the contaminant. Then, the articles are exposed tothe active regions of a resonant ultrasonic transducer stack whilesimultaneously facilitating mild turbulence of the slurry to asufficient magnitude to agitate the particles within the activeultrasonic zones.

Various structures and manners of carrying out the above-summarizedsteps are described herein. First, the particulates are confined withinthe resonant ultrasonic transducer's active region by employing at leasteither of the following arrangements:

i. Arranging sidewalls in a single chamber on the order of the diameterof the ultrasonic transducer that completely surround the activeultrasonic zone (also referred to herein as the “single chamber”embodiment);

ii. Arranging sidewalls on only two sides of the active ultrasonic zoneseparated by a distance on the order of the diameter of the active zoneand that are in motion traversing the active zone, as in flights of ascrew feeder, separated by a pitch distance p, as depicted in theschematic illustration shown in FIG. 1 (also referred to herein as the“screw feeder” embodiment).

Each of these embodiments/arrangements, as well as variations thereof,is described in further detail below.

In each version, simultaneous agitation is applied to the confinedultrasonic regions or zones, individually, in combination, or insequence from: (i) dynamic pressure gradients achieved through fluidflow; (ii) the mechanical motion of the aforementioned confiningsidewalls; and/or (iii) the action of the ultrasound assisting informing migrating particles within the confined treatment zone.

The ultrasound treatment is carried out by employing ultrasonicfrequencies preferably within the range of 25 kHz and 45 kHz. In thescrew feeder embodiment briefly summarized above, a series of ultrasonictransducers is placed circumferentially on the perimeter of the screwfeeding system, such as schematically shown in FIG. 2.

The treatment results in a stabilization of the removed oil and finedirt in the water and detergent in the form of: (1) a stable emulsion oftwo immiscible fluids, wherein the dispersed phase of the emulsioncontains droplets of less than 10 micrometers; (2) a stable dispersionof small solids and a fluid; and/or (3) a stable emulsified dispersionconsisting of solids and two immiscible fluids.

Preferably, the slurry contains solid particles no greater than 1 inchin any dimension. The slurry also preferably contains a water toparticle weight ratio of no greater than 10:1, or 8:1, or 5:1. Theslurry further preferably utilizes mild detergent concentrations ofgreater than 0.2% weight of water.

In accordance with the present invention, the above-summarized “singlechamber” embodiment entails cleaning particulates, such as titaniumchips, within an ultrasound tank. Exemplary ultrasound tanks that may beemployed are those supplied by Advanced Sonic Processing Systems, Inc.of Oxford, Conn. A photograph of an exemplary ultrasound tank and apower supply is shown in FIG. 3.

The tank chamber, which may be made of stainless steel, has, forexample, an internal volume of 400 in³, and the power supply is capableof delivering a signal of 18-20 KHz and 300-500 watts of alternatingcurrent power to two magnetostrictive transducers located on the tank'sbottom. Of course, other ultrasound tanks having different volumes andpower supply requirements, and a different number of transducers, may beemployed. During operation, the vibration of the transducers produces anultrasound signal that is transmitted into a bath of water in the tank.

During testing of the present invention, two different types of rawtitanium machining chips were used: (1) a first type from a conventionalmachining source with an average particle length of around 10 mm (hereinidentified as “conventional” chips) and shapes ranging from flat platesto curlicues; and (2) a second type from a finer variety of roughly 1 mmchips produced from electron discharge machining (herein identified asthe “fine” chips). A quantity of chips was placed in a casserole-sizedish, and warm water was poured over the chips within the dish. The dishwas placed inside the tank (or “chamber”) on top of a water bath about 2inches high. The transducers were powered, resulting in the ultrasoundsignal, which in turn caused progressive removal of oil from the chips.During testing, the water gradually became milky, which was anindication of oil being removed from the chips by the ultrasound energy.

In accordance with the present invention, portions of the chips thatresided in the herein-called “ultrasound active zones” (or, simply,“active zones”) responded to the ultrasound substantially more thanthose portions of the chips that resided outside the active zones (forconvenience, such areas outside the active zones are referred to hereinas “dead zones”). In other words, chips that resided within the deadzones lay reasonably dormant within the tank and accordingly far lessoil was removed from those chips as compared to the amount of oil thatwas removed from the chips within the active zones.

Moreover, the rates of oil removal from the two different types of chips(i.e., the conventional chips and the fine chips) are substantiallydifferent. For the fine chips, the rate of removal is substantiallyhigher, wherein during testing there were intense plumes of oil duringcleaning of the fine chips. For the conventional chips, the rate ofremoval, while still high as compared to prior art techniques, is lowerthan that for the fine chips, most likely due to the differences intotal surface area between the two types of chips.

FIGS. 4A through 4D, a series of photographs, show the progress incleaning a sample of titanium chips during the passage of time inaccordance with the present invention. FIG. 4A shows a clear slurry atthe initial state. FIG. 4B shows, at the onset of the ultrasoundcleaning process, the rapid development of a milky appearance of theslurry. FIG. 4C shows the slurry after 1 minute of cleaning. FIG. 4Dshows the slurry after 5 minutes of cleaning. Thus, as shown in thesephotos, the water gets progressively milkier, evidence of the gradualremoval of oil from the chips, as time progresses.

Preferably, during the herein-described treatment of contaminated chips,the water is maintained at a temperature of between 115 and 120 degreesFahrenheit, in order to increase the rate of oil removal from the chips.However, at higher temperatures, the herein-described treatment processstill results in effective removal of contaminants from particulates.

In addition, a small amount of preferably biodegradable, mild detergent,such as mild dishwashing liquid, may be added to the bath (i.e., thedish within the tank). The presence of the detergent results in anincreased cleaning rate of the chips as compared to treatment withoutdetergent. For example, a standard amount of detergent at 0.2 weight %of the amount of water may be added to each batch being cleaned.However, when circumstances warrant it, such as with substantially oilymetal chips, a higher amount of soap, but not exceeding 1.0 weight % ofwater, may be used. Unlike the prior art, where substantial soapadditions are made to the process water for the specific purpose ofreacting with the oil adhering to the metal chips and thereby removingthe oil, in this application the soap addition serves solely as anemulsifier for the oil removed from the chips. No cleaning functionaccompanies the soap addition in this process.

Water to chip weight ratios of 10:1, 8:1 and 5:1 were successful duringthe herein-described treatment. The lower ratios may be preferred sincethey require smaller containment areas in which to treat the same volumeof particulates.

In connection with this embodiment of the present invention, the dishcontaining the particulates may cause, depending on what it is made of(e.g., glass), a reduction in the amount of ultrasound energy that isapplied to the particulates themselves (thus resulting in reducedefficacy of the treatment). Therefore, the present invention includesthe appreciation of the structure, design and materials of the vessel inwhich the contaminated particulates are contained during such treatment.Accordingly, in a variation of the above-described embodiment, the chipsmay be contained within the ultrasound tank itself during theirtreatment.

As mentioned above, the inventors hereof have recognized the existenceof active and dead zones of the ultrasound. In accordance with thepresent invention, the structure, shape and design of the vesselcontaining the particulates (the “containment vessel”) during treatmentpreferably should contain the contaminated particulates (or the bulk ofthe contaminated particulates) within the active zone(s) of theultrasound. FIG. 5 is a photograph of a sheet of aluminum foil that hasundergone “treatment” within the ultrasound tank. The eroded/destroyedareas of the foil correspond to active zone(s) or regions of highultrasound intensity. The other portions of the foil (that remainedintact) were not exposed to ultrasound and correspond to the dead zones.

The foil shown in FIG. 5 was placed at the bottom of the ultrasoundtank. Additional tests included placing individual sheets, verticallyand horizontally, at different locations within the tank. In eachinstance, active and dead zones were detected. In accordance with thepresent invention, it was discovered that a single, highly active zoneexists in the center of the ultrasound chamber, wherein during testingone very large hole was created in a foil placed upright in the centerof the chamber. FIG. 6 shows a schematic illustration of that singleactive zone, which is located a distance from the bottom of theultrasound tank.

In accordance with the present invention, the particulates should bemaintained inside the above-described highly active zones, or at leastwithin sufficiently active zones, inside the treatment chamber tomaximize the effectiveness of the process. During testing, a sample oftitanium chips was manually held within the aforementioned highly activezone and, during treatment, the chips were cleaned very quickly.

However, the inventors hereof discovered that treating a sample of chipswithin a container that is positioned freely within the active zoneresults in the chips' movement, upon application of the ultrasound, tothose portions of the container in which the ultrasound field was eithernon-existent or smallest. During testing, the chips quickly accumulatednear the sides of the container where the ultrasound was weakest (ornon-existent). This resulted in a substantial reduction in cleaning rateas compared to the above-described situation of treating samplesmanually held within the active zones. Moreover, due to the chips' smallsize (i.e., with dimensions smaller than about 1 inch), many chipswithin the container are able to (and, in fact, do) assemble within allavailable dead zones, thereby reducing the efficacy of the treatment.This problem is not encountered or only minimally deleterious ifsubstantially large objects are treated by the herein-described process.

Accordingly, and in accordance with the present invention, treatment ismaximized when the particulates to be cleaned are disposed or confinedfor a sufficient amount of time within the active portion of theultrasound field. Therefore, the present invention employs a containmentchamber that is itself fully disposed within the active zone of theultrasound field to ensure that the contained particulates are withinthe active zone during treatment. Accordingly, if the walls of thecontainment chamber are of a sufficient arrangement so that thecontained material is completely within the active zone of theultrasound (which is the above-summarized “single chamber” embodiment),then treatment of the particulates within the containment chamber ismaximized, as herein described.

In a version of the above-described single chamber embodiment, multiple“single chambers” are arranged on a conveyor belt type arrangementwherein each chamber, having particulates stored within, is transportedthrough one or more ultrasound fields in order to clean the particulateswithin the chambers. In such version, each chamber is loaded with a setamount of particulates to be cleaned at an initial, loading position,then moved through the active portion of an ultrasound field, andfinally moved to an unloading position, where the treated particulatesare removed from the chamber. By using a conveyor belt type arrangement,multiple chambers may be employed simultaneously, in succession, whereeach chamber passes one at a time (or two at a time, or three at a time,etc.) through the active portion of the ultrasound field. Water, with orwithout the above-mentioned detergent, can be manually placed within andremoved from each chamber for each pass. For relatively largeoperations, it may be preferable to pump water through each of thechambers automatically during operation. In addition, the ultrasoundfield may be comprised of multiple ultrasound fields.

Turning now to the screw feeder embodiment briefly summarized above,FIGS. 7 and 8 schematically illustrate the operation and structure ofthe screw feeder embodiment of the present invention.

FIG. 7 is a schematic illustration of the system 10 for treatingparticulate solids in accordance with the screw feeder embodiment of thepresent invention, and FIG. 8 shows a portion of the system. Initially,a supply of raw chips 2 (i.e., particulates to be treated) is loadedinto a hopper 12. Hopper 12 preferably is conical in shape and may bemade out of steel or other suitable material. The raw chips 2 exit thebottom 13 of the hopper at a desired flow rate and drop into ahorizontally disposed tube 14. An auger 16 is disposed within the tube14, such as shown in FIGS. 1 and 2. Tube 14 and auger 16 collectivelyare referred to as screw feeder device 16 (or, simply, the screwfeeder). Auger 16 is suitably sized relative to the width of tube 14 sothat chips are unable to pass through any space (which is substantiallysmall relative to the size of the chips) that exists between the bladesof the auger and the tube. Preferably, the thicknesses of the blades,called flights in the screw feeder, and their spacing have uniform andwell-defined geometries.

The raw chips 2, now disposed within screw feeder 16, encounter water 4to form a slurry 18. Water 4 may flow or counter-flow through screwfeeder 16. In the counter-flow version, water is introduced at a waterentrance end 30 and exits, as liquid by-product 34, at water exit end32. In the flow version, the water entrance and exit ends are reversed.Water that is introduced into the system, in both the flow andcounter-flow versions, is fresh water. However, the present inventionentails water recycling versions, which are discussed in detail below(with reference to FIGS. 9-12).

A variable speed motor 20 (shown in FIG. 8) causes the slurry 18 to movealong tube 14 (to the right in FIG. 7) at a defined rate. A series ofultrasound transducers 22 (stacks 22) are disposed along a section ofthe screw feeder's tube 14 that treat the chips in the manner describedherein. The treated chips then are separated from the liquid-by-productby filtration and are subsequently dried and stored within clean chipstorage 24. The dried, treated chips are then packaged for subsequentuse (or reuse/recycling). FIG. 8 shows exemplary dimensions of hopper 12and various other components of the system, but it is understood thatother suitable dimensions may be employed.

During operation, the variable speed motor 20 preferably can operate atdifferent speeds to enable the treatment of raw chips at rates ofbetween 24 to 240 pounds of chips per hour. In general, operation at thelow end of this range can be utilized, for example, to demonstrate thetreatment operation of the system, whereas operation at the upper end ofthis range may be suitable for the day-to-day operation of asemi-commercial plant.

Referring again to FIG. 2, this schematic illustration shows a set ofstacks of transducers mounted along the tube. Each stack is positionedabove two adjacent blades/flights of the screw feeder such that thediameter of the transducer cross-section equals the pitch of the screwfeeder. With such configuration, a slurry of chips and water flowingbetween the transducers is attacked by a strong stream of ultrasoundacross the entire pitch of the screw feeder. Advantageously, and inaccordance with the present invention, the chips are confined within thetube and between the blades of the screw feeder in such a manner thatthe chips remain in the active field of the ultrasound. Moreover, theslurry, in addition to being moved by the rotation of the screw feeder,is gently stirred and rotated by such movement thereby exposing allsides and crevices of each chip to the ultrasound field. Preferably, thescrew feeder flight design causes slight turbulence to the slurry thuscausing the chips to being meaningfully stirred and rotated during theirflow through the tube.

As described herein, the process and system for treating particulatesolids of the present invention entail, in certain embodiments, thefollowing features: (1) formation and transport of a slurry of theparticulates and water using a screw feeder; (2) screw feeder flightsthat produce a turbulence in the slurry to cause the particulates to bestirred and rotating as they move through the tube; (3) at least onetransducer stack, but preferably multiple stacks, mounted on the outsideof the tube of a certain size so that the diameter of each transducerelement equals the screw feeder pitch (i.e., the distance betweenadjacent flights); (4) the stirred, rotating chips in the slurry aregiven an intense dose of ultrasound energy so that the chips are treatedas described herein; and (5) the number of transducer stacks can bemodified as needed based on the particular application as well asdifficulty of removing the component of interest (e.g., contaminant).

Moreover, as described herein, the present invention entails exposing aset of chips to an intense field of ultrasound wherein the arrangementand sizes of the various components of the system cause the chips to becontained within the active field of the ultrasound for a sufficientperiod of time. In the screw feeder embodiment, the chips to be treatedare contained within a suitably sized tube and between adjacent flightsof the screw feeder so that the chips are unable to escape exposure tothe radiation.

Comparison to the state of the art treatment of titanium machining chipswith the present invention can be made with at least 2 performancemetrics that are: (1) treatment of three different classes of titaniumchips in accordance with certain embodiments of the present inventionachieves industry-acceptable results, as demonstrated by after-treatmentanalysis of the treated chips, with the treated chips containing as lowas 0.015% carbon.; (2) a pH of the attendant liquid by-product usedduring treatment in accordance with the present invention that remainsvery close to neutral [7.0], and occasionally rising to a maximum ofabout 8.0, as compared to pH levels in the vicinity of 11 for the liquidby-product of prior art techniques.

The improvements over prior art treatment techniques would be anunexpected result by someone skilled in the art considering that theprocess uses from 0.2 up to 2.0 weight percent of a mild detergent bythe present invention, as compared to an order of magnitude highercaustic detergent usage in prior art techniques resulting in a cleaningindex for the present invention that is as high as 1,500 pounds oftreated titanium per gallon detergent, almost 20 times above theproductivity of prior art techniques. Besides, the process does notrequire elevated temperatures or long residence times. The almostneutral condition and degree of dispersion or emulsification of thecontaminant into the attendant water permits easy disposal.

In accordance with the present invention, the herein-described processand system for treating particulate solids of the present inventionfurther entail partial or full recycling of the liquid-by-product, asfurther discussed below.

The metal chip cleaning process of the present invention employs noalkaline reagents. Hence, the liquid by-product from the reactor is veryclose to the neutral condition [pH=7] and, therefore, the liquidby-product does not need neutralization. Rather than discard the liquidby-product, it can be processed for the recovery of its retained oilbut, moreover, it is recycled as herein described.

Referring to FIG. 9, a schematic representation of the steady state flowof liquid and chips through the reactor with liquid by-product recyclingof the present invention is shown. The symbols 1 and c denote the liquidand chip streams entering and leaving the reactor, respectively. At thereactor exit (see also FIG. 7, water exit end 32), a portion of theliquid by-product, I₁ is withdrawn for separate treatment while theremainder I₂ is returned to the reactor (see also FIG. 7, water input30). At the reactor entrance, the recycled liquid is blended with aquantity of fresh water w to form the total liquid input to the reactor.As mentioned above, the water may flow or counter-flow through the screwfeeder. In the flow version, water input 30 and water exit end 32 shownin FIG. 7 are reversed, as are the directions of the arrows representingwater flow in FIG. 9, as well as in FIG. 10.

Recycling liquid to the reactor is accompanied by the return of oilpreviously removed from other chips. To avoid recontamination of thefreshly cleaned chips in the reactor, a suitable quantity of detergentis added to the liquid stream entering the reactor.

In this mode of partial liquid recycle of the present invention, the netwater to chip ratio [w/c] declines with operating time and can reach anacceptable level of 2-3 within eight hours of reactor operation. Thequantity of oil in the liquid by-product is calculated to remain below 4volume percent while the reactor is operated in the partial recycle modefor up to eight hours. Afterwards, the total amount of recycled liquidshould be taken for separate processing for oil recovery and the reactorrestarted with a fresh supply of water.

FIG. 10 shows an exemplary steady state flow of liquid and chips throughthe reactor employing an overall w/c ratio of 10. A chip supply of 1pound per hour [c=1] therefore results in a total amount of liquidentering and leaving the reactor of 10 pounds per hour [I=10]. In theexample shown in FIG. 10, 80 percent of the liquid by-product leavingthe reactor is recycled and returned to its inlet. Therefore, 8 poundsper hour [I₂=8] recycled liquid is used. This returned liquid issupplemented by 2 pounds per hour of fresh water [w=2]. At the outlet, 2pounds of by-product is permanently removed from the reactor [I₁=2] andoptionally, subsequently processed further for recovery of the oil.

For purposes of assessing the oil content of the liquid by-product, theincoming metal chips are assumed to initially contain 3.95 weightpercent carbon as an indication of their oil content. Generally, thiscarbon content corresponds to the case of the dirtiest chips ordinarilyfaced in cleaning operations. Mass balance calculations were performedfor the reactor operating for eight consecutive hours, which mayrepresent a typical operating shift for a reactor. The oil content ofthe outgoing reactor liquid by-product was calculated from the total ofthe oil content of the re-entering liquid plus the quantity of oilremoved from the chips during their passage through the reactor. Thiscalculation sequence was continued for each succeeding hour of the eighthour working shift.

FIG. 11 shows the calculated oil contents of the liquid by-product as afunction of reactor operating time. The oil contents are expressed bothin weight and volume percents. As shown, the oil content on both basesrises monotonically with time. At first, the rise is sharp but then itgradually tapers. At the end of eight hours of reactor operation, theoil content of the by-product liquid is 1.94 wt. percent, andequivalently 2.42 vol. percent.

Full recycling of the liquid by-product may be employed. In such case,the total amount of liquid by-product is recycled with no removal ofby-product and no supply of fresh water. Using a w/c of 10 and a chipinput rate of 1 pound per hour [c=1], such as was the case in the priorexample discussed above, the total amount of liquid entering and leavingthe reactor is 10 pounds per hour [I=10], but the entire amount ofliquid is recycled [I₂=10] with no by-product removed [I₁=0].

The results of full recycling are shown in FIG. 12, where it is seenthat the oil contents of the liquid by-product [on both bases] rise inlinear fashion with time during the 8 hour operating shift sequence. Atthe end of the shift, the oil content of the liquid by-product wasslightly over 3.7 weight percent and almost 4.7 volume percent.

Given the results of the examples discussed above, employing partialliquid recycling in the present invention beneficially results in oilcontents of the liquid by-product (on both percent bases) that arerespectively one half of those calculated for the case of completeliquid recycle. Moreover, partial liquid recycling results in a net w/cratio for metal chip cleaning of almost 3, much lower than that if noliquid recycle is employed.

As mentioned above, recycled liquid contains oil previously removed fromother chips. Prior to re-introducing the recycled liquid to the reactor,an appropriate quantity of detergent is added to the recycled liquid toemulsify and stabilize the oil.

In FIG. 13, a downward trend in oil content of liquid by-product isshown as the carbon content of the chips declines for the case of 80percent liquid recycle. As shown, a declining oil content of the chipsleads to less oil in the liquid. For example, chips bearing 0.55 weightpercent carbon are associated with a liquid by-product of 0.27 weightpercent and 0.34 volume percent oil.

Recycling of liquid by-product in combination with the herein-describedprocess/system for treating particulate solids beneficially reduceswater use, but provides further benefits including yielding a relativelylow oil level in the liquid by-product, and little to no concern withchip recontamination due to the use of a suitable detergent. Moreover,the partial removal of liquid by-product from and the addition of freshwater to the reactor, both in small amounts, act as control agents tolimit the growth of oil content of the by-product during successiverecycling steps. And, as discussed above, compared to the w/c ratio of10 for the reactor with no recycle (under certain circumstances), thevalue of this parameter for 80 percent liquid recycle is nearly 3.

Whether the present invention is employed with no recycling, partialrecycling or full recycling, the liquid by-product ideally possesses analmost neutral pH [7-8] and thus poses no danger to either the reactorcomponents or workers. In contrast, the liquid by-product ofconventional chip cleaning processes has a pH in the range of 11-12.

Having described various embodiments of the present invention, as wellas variations thereof, the present invention may be modified and appliedin different ways than those described herein. In particular, thepresent invention can be applied to treat other materials includingparticulates of austenitic stainless steels, nickel based super-alloys,aluminum and zirconium to name a few. In addition, the contaminant to beremoved from the particulates by the present invention may be, but isnot limited to, oil, scale, cutting fluids, solder, industrial productmarkings, and coatings. Moreover, the present invention may also beapplied to treat sand particles containing embedded petroleum-baseddroplets, such as tar, oil, and waxes. Finally, the present inventionfurther may be applied to printed circuit board particles for recoveryof embedded solder beads and remnants of copper wiring.

Therefore, it is understood that other expedients known to those skilledin the art or disclosed herein may be employed without departing fromthe spirit of the invention. It is thus intended that the appendedclaims be interpreted as including the embodiments described herein, thealternatives mentioned above, and all equivalents thereto.

What is claimed is:
 1. A system for treating particulate solids,comprising: an ultrasonic transducer producing an ultrasound signal; arotating screw feeder having a portion extending through an activeregion of the ultrasound signal produced by the ultrasonic transducer,the screw feeder having a plurality of flights each separated from oneanother by a predetermined distance that is no greater than a width ofthe active region of the ultrasound signal; and a slurry including waterand the particulate solids disposed within the screw feeder in which theparticulate solids are contained within chambers defined by the flightsof the screw feeder and move along the screw feeder as the screw feederrotates, the particulate solids contained within a chamber disposedwithin the active region of the ultrasound signal being sufficientlyagitated by the ultrasound signal to cause contaminants to separate fromthe particulate solids contained within said chamber.
 2. The system ofclaim 1, comprising a plurality of ultrasonic transducers disposedcircumferentially around a perimeter of at least a portion of the screwfeeder, each of the ultrasonic transducers producing a respectiveultrasound signal.
 3. The system of claim 1, comprising a stack ofultrasonic transducers disposed along a portion of an exterior of thescrew feeder, each of the ultrasonic transducers producing a respectiveultrasound signal and having a diameter substantially the same as apitch of the screw feeder.
 4. The system of claim 1, wherein the screwfeeder, while moving the slurry, provides a turbulence to the slurry tocause the particulate solids to be stirred and rotated.
 5. The system ofclaim 1, wherein the ultrasonic transducer produces an ultrasound signalhaving frequencies substantially within a range of 25 kHz and 45 kHz. 6.The system of claim 1, wherein the slurry contains detergent in anamount of substantially no greater than 0.2 weight % of the amount ofwater.
 7. The system of claim 1, wherein the slurry contains detergentin an amount of substantially no greater than 1.0 weight % of the amountof water.
 8. The system of claim 1, wherein the water is at atemperature not exceeding substantially 120 degrees Fahrenheit.
 9. Amethod of treating particulate solids, comprising the steps of:supplying a screw feeder for transporting contaminated particulatesolids; supplying a continuous flow of water through the screw feeder;supplying the particulate solids into the screw feeder, the particulatesolids and the water forming a slurry; supplying an ultrasound signal;transporting, by the screw feeder, the slurry containing the particulatesolids through the ultrasound signal for a predetermined amount of time,the ultrasound signal through which the slurry is transported being ofsufficient size and strength to cause contaminants to separate from theparticulate solids.
 10. The method of claim 9, wherein supplying anultrasound signal comprises disposing a plurality of ultrasonictransducers circumferentially around a perimeter of at least a portionof the screw feeder, each of the ultrasonic transducers producing arespective ultrasound signal that collectively are of sufficient sizeand strength to cause the contaminants to separate from the particulatesolids.
 11. The method of claim 9, wherein supplying an ultrasoundsignal comprises disposing a stack of ultrasonic transducers along aportion of an exterior of the screw feeder, each of the ultrasonictransducers producing a respective ultrasound signal and having adiameter substantially the same as a pitch of the screw feeder.
 12. Themethod of claim 9, comprising producing, during transporting of theslurry by the screw feeder, a turbulence in the slurry to cause theparticulate solids to be stirred and rotated.
 13. The method of claim 9,wherein the ultrasound signal has a frequency substantially within arange of 25 kHz and 45 kHz.
 14. The method of claim 9, comprising addinga detergent to the slurry in an amount of substantially no greater than0.2 weight % of the amount of water.
 15. The system of claim 9, whereinthe slurry contains detergent in an amount of substantially no greaterthan 1.0 weight % of the amount of water.
 16. The method of claim 9,wherein supplying a continuous flow of water comprises supplying acontinuous flow of water having a temperature not exceedingsubstantially 120 degrees Fahrenheit.
 17. The method of claim 9,comprising recycling at least a portion of the water from a water exitend of the screw feeder to a water entrance end of the screw feeder. 18.The method of claim 17, comprising adding detergent to the recycledwater sufficient to prevent recontamination to the particulate solids bythe contaminants disposed within the recycled water.
 19. A system fortreating particulate solids, comprising: an ultrasonic transducerproducing an ultrasound signal; a tank having a chamber substantiallyfully disposed within an active zone of the ultrasound signal; a slurryincluding water and the particulate solids, the chamber of the tankcontaining the particulate solids of the slurry within the active zoneof the ultrasound signal, wherein the ultrasound signal agitates theparticulate solids disposed within the entire chamber sufficient tocause contaminants to separate from the particulate solids.
 20. Thesystem of claim 19, wherein the ultrasonic transducer produces anultrasound signal having frequencies substantially within a range of 25kHz and 45 kHz.
 21. The system of claim 19, wherein the slurry containsdetergent in an amount of substantially no greater than 0.2 weight % ofthe amount of water.
 22. The system of claim 19, wherein the slurrycontains detergent in an amount of substantially no greater than 1.0weight % of the amount of water.
 23. The system of claim 19, wherein thewater is at a temperature not exceeding substantially 120 degreesFahrenheit.